Robert Queener & John Miller / /

Teams Direct Routing FAQs

Direct routing is the architectural term where MS Teams customers use a telecom service provider other than Microsoft for their trunking to the Public Switched Telephony Network. This architecture is common amongst larger, centralized organizations. 

We get lots of questions on Direct Routing and are sharing some of the answers here. If you'd rather read a primer on the differences between Direct Routing and Calling Plans, see


1. Can we have a hybrid setup where some numbers are on Direct Routing and some are on Calling Plans? 
        a. Yes, Direct Routing is a common set up for numbers or users that rely on analog or legacy solutions that are not supported in Teams (Call Center Software). Calling Plans are ideal for mobile information workers.

2. Can we have a hybrid setup between our telecom provider (they continue to host some numbers on their PBX, we host other numbers in a Direct Routing setup? 
      a. Yes, a Session Border Controller can intermediate between the islands. However, there may or may not be limitations as it relates to 4, 7 or 10 digit dialing. Those that remain in the PBX environment will not be able to dial by name.

3. Can there be a mix of SBCs, physical and virtual?
     a. Yes, however we recommend the same vendor with similar sizing and licensing (ie, Audiocodes for Virtual and appliance)

4. Is there a limit as to how many SBCs can be used for redundancy?
     a. No. however, we have found that two SBC’s are often sufficient enough.

5. Regarding concerns of traffic hair pinning over ISP links for users dialing from home…
     a. Can SBCs be configured in active/standby mode? Such that we could host a primary SBC in Azure and a secondary SBCs on-prem?
            i. Yes
     b. Or if they have to be in an active/active mode, can routing be customized amongst users to go to different SBCs based on their typical location?
           i. Outbound Calling from Teams: Yes, you can create two (2) Online Voice Routing Policies. The first policy would route to the on prem and then to the online in the event of a failure. The second would route to the online first then the on premise in the event of a failure.
          ii. Inbound Calling to Teams: If the SIP Trunk vendor can setup the two (2) SIP Trunks with different sets of numbers "homed" on them and if a SIP Trunk goes down that they'd automatically re-route inbound calls over the other SIP Trunk, yes. If not, you could hack something together for the case where they can only route all numbers to SIP Trunk A and on prem SBC and only route to Trunk B and online SBC if Trunk A fails or is overloaded.

6. For virtual SBCs…
       a. What are typically required specs?
            i. 64Bit CPU 2.8Ghz or greater
            ii. 16GB RAM
            iii. VMWare ESXi 5.5 or later
            iv. Hyper V on Server 2012 R2 or later
            v. 10GB of storage
     b. How do they scale as more users come online?
            i. We recommend building out the virtual appliance based on sessions to be used an account for growth. It is all based on the coder profiles (G.711, G.722, Silk) used. The less intensive the codec, the more sessions you can have.
     c. How are they packaged? Software to install in Windows/Linux? Are there OVA options?
           i. Audiocodes provides an OVA for VMWare and VHD for Hyper V. Azure based are in the Azure Marketplace

7. How often do SBCs tend to need software updates & config changes? How involving is that?
      a. AudioCodes puts out SBC Updates irregularly. They seem to always have a Long Term Support (LTS) and a Latest Release version. AC recommends that customers use the LTS version unless they need a new feature in the LR version. Looking at the 7.2 LTS's, they have come out on:
8/3/20, 10/25/20, 11/5/20, 12/17/20, 12/28/20, 1/11/21 - So quite irregularly - 15 in 2020 and 13 in 2019.
     b. once it's configured you will rarely change the configuration. If you use TLS for management or authentication and encryption, you will every few years have to update your certificate and update the Root Chains as required. If you are using Dial Plans and doing a migration, you will be touching the SBCs to update the Dial Plans each time you do a migration

8. How much do SBCs typically cost?
     a. Costs vary depending on the complexity of the design, number of users, needed High Availability or Survivability

9. What SBC vendors do you recommend? Do you know of any that offer trials? At least for their virtual appliance options?
     a. Here’s a link to the certified SBC’s

          ii. Yes. For one, AudioCodes does often provide their gear at no cost for a Proof of Concept, we have deployed Audiocodes VMWare based SBCs for Proof of concepts in the past as well.

Work with our team of Cloud Computing Consultants who have done this so many times they know all of the “minefields” to prevent missteps.